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@Article{EspinosaSarmientoPadiAlve:2019:CaStLo,
               author = "Espinosa Sarmiento, Karen Viviana and Padilha, Antonio Lopes and 
                         Alves, Livia Ribeiro",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)}",
                title = "Effects of ionospheric conductivity and ground conductance on 
                         geomagnetically induced currents during geomagnetic storms: case 
                         studies at low-latitude and Equatorial regions",
              journal = "Space Weather",
                 year = "2019",
               volume = "17",
               number = "2",
                pages = "252--268",
                month = "Feb.",
             abstract = "Geomagnetic field variations recorded by fluxgate magnetometers 
                         are used to evaluate geomagnetically induced currents (GICs) under 
                         the equatorial electrojet (EEJ) and South Atlantic Magnetic 
                         Anomaly (SAMA) during two geomagnetic storms in March and June 
                         2015. Geomagnetic stations with information about the underground 
                         electrical conductivity structure and that can be approximated by 
                         unidimensional (1-D) models for calculation of the geoelectric 
                         field are selected. GICs levels are estimated using a realistic 
                         local power grid model located in the central region of Brazil, 
                         artificially moved to the sites where the geomagnetic measurements 
                         are available. GIC magnitudes are not large during the storms, and 
                         a maximum amplitude of 3.8 A was estimated at an equatorial 
                         station positioned over high resistivity underground during the 
                         main phase of the June storm. Effects of the ionospheric currents 
                         over the measurement sites and of the conductivity distribution 
                         beneath these sites are also evaluated. It is observed that both 
                         (EEJ) and (SAMA) increase the GICs amplitudes, with the greatest 
                         effects associated with daytime (EEJ) currents. A cutoff frequency 
                         was identified for both the (EEJ) and (SAMA) so that signals with 
                         frequencies lower than 2 mHz (periods longer than 500 s) are not 
                         amplified by the ionospheric currents. In relation to the 
                         underlying conductivity structure, GIC magnitude is affected by 
                         variation of the surface impedance and the sampling rate of the 
                         geomagnetic field. In our case, differences in amplitude of the 
                         surface impedance at the Nyquist frequency control the relative 
                         effects of the ground conductance between the stations.",
                  doi = "10.1029/2018SW002094",
                  url = "http://dx.doi.org/10.1029/2018SW002094",
                 issn = "1542-7390",
             language = "en",
           targetfile = "Espinosa_et_al-2019-Space_Weather.pdf",
        urlaccessdate = "05 dez. 2020"
}


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